This invention relates to a computer system including a computer and a storage subsystem, and more particularly, to a technique of managing the configuration of the computer system.
Storage area network (SAN) is a known technology which couples at least one external storage subsystem and at least one computer. The storage area network is effective particularly when a plurality of computers share one large-scale storage subsystem. A storage system containing the storage area network is easy to add or remove a storage subsystem or a computer, and accordingly has high scalability.
Disk array devices are often commonly used as an external storage subsystem coupled to a SAN. A disk array device is equipped with a plurality of storage devices (e.g., magnetic disk drives), typically, hard disks.
A disk array device manages several magnetic disk drives as one RAID group by a technology called redundant array of independent disks (RAID). A RAID group forms at least one logical storage extent. A computer coupled to a SAN executes data input/output processing in the storage extents. When recording data in the storage extents, the disk array device records redundant data in magnetic disk drives that constitute the RAID group. The redundant data enables the disk array device to recover data even when one of the magnetic disk drives breaks down.
Data archiving systems for long-term archiving have lately become popular as a measure to preserve contract documents, official documents, and the like for a long period of time. These data archiving systems have functions such as data protection (WORM), data location management, data deduplication, and quick search to provide a mechanism for preserving and managing data properly for years (see WO 2005/043323).
Data deduplication reduces the amount of data held in a system when a plurality of computers in the system hold the same data redundantly, by allowing only one of the computers to keep the data and giving the rest of the computers a reference to the unique copy (data storage location in a storage extent).
In data archiving systems which are kept in operation for a long time, adding computer resources and replacing a failed component with a new one are expected at some point in future. There may be a difference in performance between a newly introduced computer and a computer that has existed in the system.
The newly introduced computer in some cases is given a smaller amount of data to manage than the existing computer despite the new computer's superior performance. Also, if frequently accessed data is stored in the older computer, the concentration of load on the computer of inferior performance lowers the overall performance of the system. A load concentration on a low-performance server can occur also when data amount reducing processing such as deduplication changes the access frequency of the respective pieces of data and destroys the performance-based load balance among computers.
As a solution, data migration techniques are disclosed in JP 2006-228188 A and JP 2004-139200 A, where data is migrated from a heavy-load computer to a light-load computer in order to balance the load among a plurality of computers in a data archiving system and to thereby improve the performance of the system.